Cycling, as a way of travel and sports, becomes more and more popular. And helmet becomes a standard configuration for a cycling hobbyist. In order to satisfy needs of different cycling hobbyists, the helmet is various. A kind of luminous helmet can emit light for both decoration and warning. In prior, aluminous helmet includes a light source, which is set on a surface of the luminous helmet or arranged in a groove defined from the surface into the luminous helmet. There are a variety of disadvantages of such luminous helmet, for example the luminous helmet may have a bad appearance because of the exposed light source and the exposed light source may be easily damaged as a result of external impact. In order to avoid these disadvantages, a helmet with hidden light source is desired.